Catalytic boracarboxylation of alkynes with diborane and carbon dioxide by an N-heterocyclic carbene copper catalyst

Catalytic Regio- and Enantioselective Remote Hydrocarboxylation of Unactivated Alkenes with CO2

The catalytic regio- and enantioselective hydrocarboxylation of alkenes with carbon dioxide is a straightforward strategy to construct enantioenriched α-chiral carboxylic acids but remains a big challenge. Herein we report the first example of catalytic highly enantio- and site-selective remote hydrocarboxylation of a wide range of readily available unactivated alkenes with abundant and renewable CO2 under mild conditions enabled by the SaBOX/Ni catalyst. The key to this success is utilizing the chiral SaBOX ligand, which combines with nickel to simultaneously control both chain-walking and the enantioselectivity of carboxylation. This process directly furnishes a range of different alkyl-chain-substituted or benzo-fused α-chiral carboxylic acids bearing various functional groups in high yields and regio- and enantioselectivities. Furthermore, the synthetic utility of this methodology was demonstrated by the concise synthesis of the antiplatelet aggregation drug (R)-indobufen from commercial starting materials.

Copper Catalyzed Borylation of Alkynes: An Experimental Mechanistic Study

The copper catalyzed hydroboration of alkynes with B2pin2 was studied by in detail studies of individual relevant steps along the catalytic pathway. A number of reaction steps were retraced by in situ NMR spectroscopy as well as central intermediates and side-products were isolated and comprehensively characterized. A copper boryl complex is central to the catalytic process by inserting the terminal alkyne substrate into the B-Cu bond. The selectivity of this step - depending on the NHC auxiliary ligand - determines the α/β selectivity observed in the product. The latter complex is protonated by the auxiliary alcohol reagent resulting in hydroboration product formation and formation of a Cu alkoxido complex. Reaction of the latter with B2pin2 results in the regeneration of the central copper boryl complex. This alcoholysis step depends on the acidity of the alcohol, in particular on the relative acidity of the alcohol vs. the alkyne substrate. A number of side reactions leading to the hydrogenation product of the alkyne substrate and a bis hydroborated product were identified and studied in some detail. It is concluded that the performance of a particular catalytic system depends crucially on the relative acidities of the reagents and generalizations may be difficult.

Access to Cyclic Borates by Cu-Catalyzed Borylation of Unactivated Vinylcyclopropanes

We report the copper-catalyzed borylation of unactivated vinylcyclopropanes to form six-membered cyclic borate salts. A copper complex bearing an N-heterocyclic ligand in combination with bis(pinacolato)diboron and LiOtBu catalyzes the ring-opening of the substrate under mild reaction conditions. The protocol can be applied to aryl- and heteroaryl-substituted vinylcyclopropanes and can be conducted on a gram scale. The synthetic utility of the lithium salts of the cyclic borate has been demonstrated through regioselective ring-opening functionalizations.

Copper-catalyzed remote double functionalization of allenynes

Addition reactions of molecules with conjugated or non-conjugated multiple unsaturated C-C bonds are very attractive yet challenging due to the versatile issues of chemo-, regio-, and stereo-selectivities. Especially for the readily available conjugated allenyne compounds, the reactivities have not been explored. The first example of copper-catalyzed 2,5-hydrofunctionalization and 2,5-difunctionalization of allenynes, which provides a facile access to versatile conjugated vinylic allenes with a C-B or C-Si bond, has been developed. This mild protocol has a broad substrate scope tolerating many synthetically useful functional groups. Due to the highly functionalized nature of the products, they have been demonstrated as platform molecules for the efficient syntheses of monocyclic products including poly-substituted benzenes, bicyclic compounds, and highly functionalized allene molecules.

Catalytic Regio- and Enantioselective Boracarboxylation of Arylalkenes with CO2 and Diboron

Catalytic asymmetric carboxylation of readily available alkenes with CO2, an abundant and sustainable one-carbon building block, that gives access to value-added α-stereogenic carboxylic acids in an atom- and step-economic manner is highly attractive. However, it has remained a formidable challenge for the synthetic community. Here, the first example of Cu-catalyzed highly regio- and enantioselective boracarboxylation reaction on various arylalkenes with diboron under an atmospheric pressure of CO2 is described, which afforded a variety of chiral β-boron-functionalized α-aryl carboxylic acids with up to 87% yield and 97% ee under mild conditions. Importantly, α-substituted arylalkenes could also be subject to this protocol with excellent enantiopurities, thereby rendering an efficient approach for the generation of enantioenriched carboxylic acids with an α-chiral all-carbon quaternary center. Moreover, high functional group tolerance, scalable synthesis, and facile access to bioactive compounds, like (-)-scopolamine, (-)-anisodamine, and (-)-tropicamide, further demonstrated the synthetic utility of this strategy.

Cu-Catalyzed Asymmetric Dicarboxylation of 1,3-Dienes with CO2

Dicarboxylic acids and derivatives are important building blocks in organic synthesis, biochemistry, and the polymer industry. Although catalytic dicarboxylation with CO2 represents a straightforward and sustainable route to dicarboxylic acids, it is still highly challenging and limited to generation of achiral or racemic dicarboxylic acids. To date, catalytic asymmetric dicarboxylation with CO2 to give chiral dicarboxylic acids has not been reported. Herein, we report the first asymmetric dicarboxylation of 1,3-dienes with CO2 via Cu catalysis. This strategy provides an efficient and environmentally benign route to chiral dicarboxylic acids with high regio-, chemo-, and enantioselectivities. The copper self-relay catalysis, that is, Cu-catalyzed boracarboxylation of 1,3-dienes to give carboxylated allyl boronic ester intermediates and subsequent carboxylation of C-B bonds to give dicarboxylates, is key to the success of this dicarboxylation. Moreover, this protocol exhibits broad substrate scope, good functional group tolerance, easy product derivatizations, and facile synthesis of chiral liquid crystalline polyester and drug-like scaffolds.

Acyclic Boryl Complexes of Copper(I)

Reaction of (6-Dipp)CuOtBu (6-Dipp=C{NDippCH2 }2 CH2 , Dipp=2,6-iPr2 C6 H3 ) with B2 (OMe)4 provided access to (6-Dipp)CuB(OMe)2 via σ-bond metathesis. (6-Dipp)CuB(OMe)2 was characterised by NMR spectroscopy and X-ray crystallography and shown to be a monomeric acyclic boryl of copper. (6-Dipp)CuB(OMe)2 reacted with ethylene and diphenylacetylene to provide insertion compounds into the Cu-B bond which were characterised by NMR spectroscopy in both cases and X-ray crystallography in the latter. It was also competent in the rapid catalytic deoxygenation of CO2 in the presence of excess B2 (OMe)4 . Alongside π-insertion, (6-Dipp)CuB(OMe)2 reacted with LiNMe2 to provide a salt metathesis reaction at boron, giving (6-Dipp)CuB(OMe)NMe2 , a second monomeric acyclic boryl, which also cuproborated diphenylacetylene. Computational interrogation validated these acyclic boryl species to be electronically similar to (6-Dipp)CuBpin.

Deconstructive Carboxylation of Activated Alkenes with Carbon Dioxide

Carboxylation with carbon dioxide (CO2 ) represents one notable methodology to produce carboxylic acids. In contrast to carbon-heteroatom bonds, carbon-carbon bond cleavage for carboxylation with CO2 is far more challenging due to their inherent and less favorable orbital directionality for interacting with transition metals. Here we report a photocatalytic protocol for the deconstructive carboxylation of alkenes with CO2 to generate carboxylic acids in the absence of transition metals. It is emphasized that our protocol provides carboxylic acids with obviously unchanged carbon numbers when terminal alkenes were used. To show the power of this strategy, a variety of pharmaceutically relevant applications including the modular synthesis of propionate nonsteroidal anti-inflammatory drugs and the late-stage carboxylation of bioactive molecule derivatives are demonstrated.

Iterative Dual-Metal and Energy Transfer Catalysis Enables Stereodivergence in Alkyne Difunctionalization: Carboboration as Case Study

Stereochemically defined tetrasubstituted olefins are widespread structural elements of organic molecules and key intermediates in organic synthesis. However, flexible methods enabling stereodivergent access to E and Z isomers of fully substituted alkenes from a common precursor represent a significant challenge and are actively sought after in catalysis, especially those amenable to complex multifunctional molecules. Herein, we demonstrate that iterative dual-metal and energy transfer catalysis constitutes a unique platform for achieving stereodivergence in the difunctionalization of internal alkynes. The utility of this approach is showcased by the stereodivergent synthesis of both stereoisomers of tetrasubstituted β-boryl acrylates from internal alkynoates with excellent stereocontrol via sequential carboboration and photoisomerization. The reluctance of electron-deficient internal alkynes to undergo catalytic carboboration has been overcome through cooperative Cu/Pd-catalysis, whereas an Ir complex was identified as a versatile sensitizer that is able to photoisomerize the resulting sterically crowded alkenes. Mechanistic studies by means of quantum-chemical calculations, quenching experiments, and transient absorption spectroscopy have been applied to unveil the mechanism of both steps.

Catalytic Alkyne Allylboration: A Quest for Selectivity

Catalytic methodologies that enable the synthesis of complex organic molecules from simple and readily available starting materials represent a goal in modern synthetic chemistry. In particular, multicomponent carboboration reactions that provide stereoselective access to densely functionalized building blocks are particularly valuable to achieve molecular diversity. This Perspective covers the developments in the area of catalytic allylboration of alkynes and highlights the key features that have allowed for the control of the regio-, diastereo-, and enantioselectivity in these transformations.

Multicomponent Reaction: Pd/Cu-Catalyzed Coupling and Boration of Acyl Chlorides and Alkynes to β-Boryl Ketones

An unprecedented and challenging multicomponent reaction has been developed that allows for the direct transformation of acyl chlorides with alkynes into the corresponding saturated β-boryl ketones via Pd/Cu-catalyzed coupling and boration with ethyl acetate as the hydrogen sources. Various β-boryl ketones were synthesized in good to excellent yields with broad functional group tolerance. In addition, the introduction of boron groups into the products provides substantial opportunities for further conversions.

Auto-Tandem Copper-Catalyzed Carboxylation of Undirected Alkenyl C-H Bonds with CO2 by Harnessing β-Hydride Elimination

The exploration into challenging scenarios of the application of elementary reactions offers excellent opportunities for the development of unique transformations under organometallic catalysis. As a ubiquitous reaction of metal alkyl complexes, β-hydride elimination plays a crucial role in a number of important catalytic transformations. However, its functions in these catalytic cycles are limited to either releasing alkene products or generating isomerized intermediates through further migratory insertion. Herein, we report that the precise manipulation of β-hydride elimination enables an auto-tandem copper catalysis for the carboxylation of undirected alkenyl C-H bonds with CO₂. In this transformation, β-hydride elimination of an alkyl copper intermediate is facilitated, while its reaction with CO₂ is suppressed. The resulting copper hydride in turn reacts with CO₂ to provide access to a multitasking catalyst, which enables the tandem borylation/carboxylation of C-H bonds in two mechanistically distinct catalytic cycles.

Regioselective catalytic carbonylation and borylation of alkynes with aryldiazonium salts toward α-unsubstituted β-boryl ketones

A new Pd/Cu-catalyzed carbonylation and borylation of alkynes with aryldiazonium salts toward α-unsubstituted β-boryl ketones with complete regioselectivity has been developed. This transformation shows broad substrate scope and excellent functional-group tolerance. Moreover, the obtained 1,2-carbonylboration products provide substantial opportunities for further transformations which cannot be obtained by known carbonylation procedures. Preliminary mechanistic studies indicate that the three hydrogen atoms of the products originated from ethyl acetate.

Development of a General Method for the Hiyama-Denmark Cross-Coupling of Tetrasubstituted Vinyl Silanes

General conditions for the Hiyama-Denmark cross-coupling of tetrasubstituted vinyl silanes and aryl halides are reported. Prior reports of Hiyama-Denmark reactions of tetrasubstituted vinyl silanes have required the use of vinyl silanols or silanolates, which are challenging to handle, or internally activated vinyl silanes, which lack structural generality. Now, unactivated tetrasubstituted vinyl silanes, bearing bench-stable tetraorganosilicon centers, and aryl halides can be coupled. The key to this discovery is the identification of dimethyl(5-methylfuryl)vinylsilanes as bench stable and easily prepared cross-coupling partners that are readily activated under mild conditions in Hiyama-Denmark couplings. These palladium-catalyzed cross-couplings proceed well with aryl chlorides, though aryl bromides and iodides are also tolerated, and the reactions display high stereospecificity in the formation of tetrasubstituted alkenes. In addition, only a mild base (KOSiMe3) and common solvents (THF/DMA) are required, and importantly toxic additives (such as 18-crown-6) are not needed. We also show that these conditions are equally applicable to Hiyama-Denamrk coupling of trisubstituted vinyl silanes.

Synthesis of gem-Difluorinated 1,3-Dienes via Synergistic Cu/Pd-Catalyzed Borodifluorovinylation of Alkynes

gem-Difluoroalkenes (=CF₂), which normally act as metabolically stable bioisosteres for carbonyl groups (C═O), are widely applied in agrochemicals and pharmaceuticals and are also used as building blocks in organic synthesis. Herein, an example of Cu/Pd-catalyzed borodifluorovinylation was achieved using alkynes, difluoroethylene bromide, and B₂pin₂ as chemical feedstocks, providing the corresponding conjugated gem-difluoroalkene scaffold with good functional group compatibility. Moreover, an array of fluorinated synthons can be obtained through further transformations.

One-Metal/Two-Ligand for Dual Activation Tandem Catalysis: Photoinduced Cu-Catalyzed Anti-hydroboration of Alkynes

A dual catalyst system based on ligand exchange of two diphosphine ligands possessing different properties in a copper complex has been devised to merge metal- and photocatalytic activation modes. This strategy has been applied to the formal anti-hydroboration of activated internal alkynes via a tandem sequence in which Cu/Xantphos catalyzes the B₂pin₂-syn-hydroboration of the alkyne whereas Cu/BINAP serves as a photocatalyst for visible light-mediated isomerization of the resulting alkenyl boronic ester. Photochemical studies by means of UV–vis absorption, steady-state and time-resolved fluorescence, and transient absorption spectroscopy have allowed characterizing the photoactive Cu/BINAP species in the isomerization reaction and its interaction with the intermediate syn-alkenyl boronic ester through energy transfer from the triplet excited state of the copper catalyst. In addition, mechanistic studies shed light into catalyst speciation and the interplay between the two catalytic cycles as critical success factors.

Cu-catalyzed carboboration of acetylene with Michael acceptors

A copper-catalyzed three-component carboboration of acetylene with B2Pin2 and Michael acceptors is reported. In this reaction, a cheap and abundant C2 chemical feedstock, acetylene, was used as a starting material to afford cis-alkenyl boronates bearing a homoallylic carbonyl group. The reaction was robust and could be reliably performed on the molar scale. Furthermore, the resulting cis-alkenyl boronates could be converted to diverse functionalized molecules with ease.

(CAAC)Copper Catalysis Enables Regioselective Three-Component Carboboration of Terminal Alkynes

Cyclic(alkyl)(amino)carbene (CAAC) ligands are found to perturb regioselectivity of the copper-catalyzed carboboration of terminal alkynes, favoring the less commonly observed internal alkenylboron regiosomer through an α-selective borylcupration step. A variety of carbon electrophiles participate in the reaction, including allyl alcohols derivatives and alkyl halides. The method provides a straightforward and selective route to versatile tri-substituted alkenylboron compounds that are otherwise challenging to access.

Dinitrogen Cleavage and Functionalization with Carbon Dioxide in a Dititanium Dihydride Framework

The activation and functionalization of dinitrogen (N₂) with carbon dioxide (CO₂) are of great interest and importance but highly challenging. We report here for the first time the reaction of N₂ with CO₂ in a dititanium dihydride framework, which leads to N-C bond formation and N-N and C-O bond cleavage. Exposure of a dinitrogen dititanium hydride complex {[(^acriPNP)Ti]₂(μ₂-η¹:η²-N₂)(μ₂-H)₂} (1) (^acriPNP = 4,5-bis(diisopropylphosphino)-2,7,9,9-tetramethyl-9H-acridin-10-ide) to a CO₂ atmosphere at room temperature rapidly yielded a nitrido/N,N-dicarboxylamido complex {[(^acriPNP)Ti]₂(μ₂-N)[μ₂-N(CO₂)₂]} (2, 28%) and a diisocyanato/dioxo complex {[(^acriPNP)Ti]₂(NCO)₂(μ₂-O)₂} (3, 52%) with release of H₂. When the reaction of 1 with CO₂ (1 atm) was carried out at -50 °C, complex 2 was selectively formed in 82% yield within 5 min. Heating 2 at 80 °C under 1 atm CO₂ for 30 min afforded 3 in 67% yield. When 1 was allowed to react with 1.5 equiv of CO₂ at room temperature, an isocyanato/nitrido/oxo complex {[(^acriPNP)Ti]₂(NCO)(μ₂-N)(μ₂-O)} (4) was exclusively formed in 89% yield within 5 min. The reaction of 4 with CO₂ at room temperature almost quantitatively yielded the dioxo/diisocyanato complex 3 within 5 min. The mechanistic details were clarified by the ¹⁵N- and ¹³C-labeled experiments and density functional theory (DFT) calculations, providing unprecedented insights into the reaction of N₂ with CO₂. A titanium-mediated cycle for the synthesis of trimethylsilyl isocyanate Me₃SiNCO from N₂, CO₂, and Me₃SiCl using H₂ as a reducing agent was also established.

Carboxylation of Alkenes and Alkynes Using CO2 as a Reagent: An Overview

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CO2 fixation reactions are of paramount interest both from economical and environmental perspectives. As an abundant, non-toxic, and renewable C1 feedstock, CO2 can be utilized for the synthesis of fuels and commodity chemicals under elevated reaction conditions. The major challenge in the CO2 utilization reactions is its chemical inertness due to high thermodynamic stability and kinetic barrier. The carboxylation of unsaturated hydrocarbons with CO2 is an important transformation as it forms high-value reaction products having industrial as well as medicinal importance. This mini-review is mainly focused on the recent developments in the homogeneously and heterogeneously catalyzed carboxylation of alkenes and alkynes by using carbon dioxide as a reagent. We have highlighted various types of carboxylation reactions of alkenes and alkynes involving different catalytic systems, which comprise mainly C-H bond activation, hydrocarboxylation, carbocarboxylation, heterocarboxylation, and ring-closing carboxylation, including visible-light assisted synthesis processes. The mechanistic pathways of these carboxylation reactions have been described. Moreover, challenges and future perspectives of these carboxylation reactions are discussed.

Challenges and recent advancements in the transformation of CO2 into carboxylic acids: straightforward assembly with homogeneous 3d metals

Transformation of carbon dioxide (CO2) into valuable organic carboxylic acids is essential for maintaining sustainability. In this review, such CO2 thermo-, photo- and electrochemical transformations under 3d-transition metal catalysis are described from 2017 until 2022.

Straightforward synthesis of [Cu(NHC)(alkynyl)] and [Cu(NHC)(thiolato)] complexes (NHC = N-heterocyclic carbene)

Synthetic access to monomeric copper-alkynyl and copper-thiolato complexes of the type [(NHC)Cu(R)] (R = alkynyl or thiolato) using a weak base approach is reported. All reported reactions proceed under mild conditions in air and in environmentally acceptable solvents. The novel complexes are fully characterized and single crystal X-ray analyses unambiguously establish the atom connectivity in these mononuclear complexes. The importance of the supporting NHC ligand's steric properties in stabilizing mononuclear complexes is discussed.

Recent advances in Cu-catalyzed transformations of internal alkynes to alkenes and heterocycles

Numerous metal-catalyzed reactions involving internal alkynes and aimed towards synthetically and pharmacologically important alkenes and heterocycles have appeared in the literature. Among these, Cu-catalyzed reactions have a special place, which has prompted the investigation and development of carbon-carbon and carbon-heteroatom bond-forming reactions. These reactions possess wide scope, and during the paths of these reactions, either stable or in situ intermediates are formed via the addition of Cu as a core catalyst or synergistic catalyst. In this review, we aim to report different contributions relating to Cu-catalyzed reactions of internal alkynes for the synthesis of different valuable alkenes and heterocycles which have appeared in the literature in the last decade. We anticipate that this appraisal will deliver basic insights for the further advancement of Cu-catalyzed reactions in organic chemistry.

A stable ring-expanded NHC-supported copper boryl and its reactivity towards heterocumulenes

Reaction of bis(pinacolato)diboron with (6-Dipp)CuO^tBu generates a ring-expanded N-heterocyclic carbene supported copper(I) boryl, (6-Dipp)CuBpin. This compound showed remarkable stability and was characterised by NMR spectroscopy and X-ray crystallography. (6-Dipp)CuBpin readily dechalcogenated a range of heterocumulenes such as CO₂, isocyanates and isothiocyanates to yield (6-Dipp)CuXBpin (X = O, S). In the case of CO₂ catalytic reduction to CO is viable in the presence of excess bis(pinacolato)diboron. In contrast, in the case of iso(thio)cyanates, the isocyanide byproduct of dechalcogenation reacted with (6-Dipp)CuBpin to generate a copper(I) borylimidinate, (6-Dipp)CuC(NR)Bpin, which went on to react with heterocumulenes. This off-cycle reactivity gives selective access to a range of novel boron-containing heterocycles bonded to copper, but precludes catalytic reactivity.

Copper-catalyzed borofunctionalization of styrenes with B2pin2 and CO

The construction of structurally complexed and high-value chemical molecules from simple and readily available feedstocks is a long-standing challenge to chemists. Here, we describe a copper-catalyzed borofunctionalization of styrenes with B₂pin₂ and carbon monoxide. A set of new sodium cyclic borates were obtained with NaO^tBu as the base. These unique sodium cyclic borates can be easily converted into a variety of multifunctional β-boryl vinyl esters, boryl carbonates, β-boryl aldehydes, and boryl vinyl ether. In addition, the procedure also features good functional group tolerance and utilizes CO as the C1 source.

A new copper-catalyzed borofunctionalization of styrenes with B₂pin₂ and carbon monoxide has been developed.

Cu/Pd-Catalyzed cis-Borylfluoroallylation of Alkynes for the Synthesis of Boryl-Substituted Monofluoroalkenes

Monofluoroalkenes normally act as metabolically stable bioisosteres for amide groups (-NH-CO-) and have widespread applications in drug discovery. Additionally, they are widely used as building blocks in organic synthesis. In this study, the Cu/Pd-catalyzed cis-borylfluoroallylation of alkynes was achieved, providing a modular and general tactic for the preparation of monofluorinated alkene scaffolds with high regioselectivity and stereoselectivity. Moreover, an array of synthetic building blocks can be generated by downstream transformations.

Light-Promoted Organic Transformations Utilizing Carbon-Based Gas Molecules as Feedstocks

Carbon-based gas molecules are readily available feedstocks and are widely used in industry as building blocks or fuels. However, their application in the synthesis of fine chemicals has been hampered due to operational complexity, poor reaction efficiency and selectivity. Recent development of photoredox-promoted transformations using such gaseous reagents has received considerable attention from the synthetic community. In this review, efforts in developing light-promoted organic transformations using carbon-based natural gases as C1 or C2 feedstocks and to overcome the associated challenges are briefly summarized.

Pivotal Electron Delivery Effect of the Cobalt Catalyst in Photocarboxylation of Alkynes: A DFT Calculation

Photocarboxylation of alkyne with carbon dioxide represents a highly attractive strategy to prepare functionalized alkenes with high efficiency and atomic economy. However, the reaction mechanism, especially the sequence of elementary steps (leading to different reaction pathways), reaction modes of the H-transfer step and carboxylation step, spin and charge states of the cobalt catalyst, etc., is still an open question. Herein, density functional theory calculations are carried out to probe the mechanism of the Ir/Co-catalyzed photocarboxylation of alkynes. The overall catalytic cycle mainly consists of four steps: reductive-quenching of the Ir catalyst, hydrogen transfer (rate-determining step), outer sphere carboxylation, and the final catalyst regeneration step. Importantly, the cobalt catalyst can facilitate the H-transfer by an uncommon hydride coupled electron transfer (HCET) process. The pivotal electron delivery effect of the Co center enables a facile H-transfer to the α-C(alkyne) of the aryl group, resulting in the high regioselectivity for β-carboxylation.

Carbon dioxide based methodologies for the synthesis of fine chemicals

Rapid environmental changes triggered by the increase in the concentration of heat-absorbing gases such as CO2 in the atmosphere have become a major cause of concern. One of the ways to counter this growing threat will be to efficiently convert atmospheric CO2 into value-added products via the development of efficient transition-metal-catalyzed processes. Conversion of CO2 into bulk products such as CH3OH and methane as well as its incorporation into commercial polyurethane synthesis has been achieved and reviewed extensively. However, the efficient transformation of CO2 into fine chemicals and value-added chemicals has many fold advantages. Recent years have seen a rapid rise in the number of metal-mediated protocols to achieve this goal of converting CO2 into fine chemicals. These are essential developments given the requirement of several commodities and fine chemicals in various industrial processes and the utilization of atmospheric CO2 will help provide a sustainable solution to the current environmental problems. Accordingly, we present here a comprehensive compilation of catalytic processes, involving CO2 as the C1 source for reacting with substrates such as alkanes, alkenes, alkynes, amines, acid chlorides, alcohols, allyl boronates, alkenyl triflates, and many others to provide easy access to a wide variety of useful molecules. Such a technology would certainly prove to be beneficial in solving the problems associated with the environmental accumulation of CO2.

Copper-catalyzed boroacylation of allenes to access tetrasubstituted vinylboronates

A distinct copper-catalyzed boroacylation of allenes with acyl chlorides and bis(pinacolato)diboron is developed. For aromatic acyl chlorides, 1,2-boroacylation of allenes readily takes place, leading to the formation of tetrasubstituted vinylboronates with exclusive (E)-stereoselectivity. In comparison, the employment of alkyl acyl chlorides as electrophiles alters the selectivity to 2,3-boroacylated products. Additionally, the product can easily undergo Suzuki-Miyaura cross-coupling to afford tetrasubstituted alkene with complete retention of the configuration.

A mechanistic study on Cu(i) catalyzed carboxylation of the C-F bond with CO2: a DFT study

The Cu(i) catalyzed carboxylation of the C-F bond recently reported by Yu and co-workers is an excellent method for the construction of complex fluoroacrylate compounds with high regioselectivity. In the present study, theoretical calculations were carried out to investigate the detailed mechanism of the catalytic cycle and the origin of regioselectivity. The calculation results reveal that the overall catalytic cycle proceeds via the migratory insertion of difluoroalkene on the boryl-Cu(i) species, synβ-F elimination, transmetalation, and carboxylation steps. The rate determining step is the carboxylation step, and the migration insertion is the regioselectivity determining step. The regioselectivity for 2,1-insertion is consistent with Yu's experiment, and is determined by both steric and electronic effects.

Mononuclear Cu Complexes Based on Nitrogen Heterocyclic Carbene: A Comprehensive Review

During the last decade, organometallic, coordination, and catalytic chemistry of the three-dimensional metals such as copper (Cu) has been greatly affected by the emergence of nitrogen heterocyclic carbene (NHC) complexes. The NHCs, and in particular the mononuclear Cu^I-based ones, have been proven vastly useful in several applications such as in biosynthesis, catalysis, photochemistry, etc. This review tries to thoroughly describe a series of mononuclear Cu^I NHC complexes and their subcategories such as heteroleptics, and bidentate and tridentate heteroatom complexes, and give some detailed insights on their development, emergence, and applications. A brief outlook is also disclosed to enable other researchers to further develop a platform for future advances and studies in the field of Cu^I-based NHCs.

Exploration of New Biomass-Derived Solvents: Application to Carboxylation Reactions

A range of hitherto unexplored biomass-derived chemicals have been evaluated as new sustainable solvents for a large variety of CO2 -based carboxylation reactions. Known biomass-derived solvents (biosolvents) are also included in the study and the results are compared with commonly used solvents for the reactions. Biosolvents can be efficiently applied in a variety of carboxylation reactions, such as Cu-catalyzed carboxylation of organoboranes and organoboronates, metal-catalyzed hydrocarboxylation, borocarboxylation, and other related reactions. For many of these reactions, the use of biosolvents provides comparable or better yields than the commonly used solvents. The best biosolvents identified are the so far unexplored candidates isosorbide dimethyl ether, acetaldehyde diethyl acetal, rose oxide, and eucalyptol, alongside the known biosolvent 2-methyltetrahydrofuran. This strategy was used for the synthesis of the commercial drugs Fenoprofen and Flurbiprofen.